1. Field of the Invention
This invention relates to ladders and specifically, to combination ladders that may be easily converted into three different basic forms, namely, a stepladder, an extension ladder and a stair well ladder.
2. Description of the Prior Art
Combination ladders that may be changed from one standard form into another, e.g., from a stepladder into an extension ladder are well known. U.S. Pat. No. 758,659 discloses an early development in combination ladders having telescoping legs so that it can be converted from a regular stepladder into a stair well ladder. However, such ladder does not convert into an extension ladder, but U.S. Pat. No. 2,152,846 discloses a stepladder which may be changed into an extension ladder.
Although wood was historically the basic material from which ladders of all types were made, light metals, such as aluminum, have now replaced wood as the principal construction material for ladders. A recent development of a combination ladder is disclosed in U.S. Pat. No. 2,899,008 so designed that it not only is convertible into either a step, extension or stair well ladder, but also includes a bucket rack.
In spite of the numerous advances that have been made in construction of combination ladders as represented by the foregoing and other prior art, there exists a continuing and strong demand in the trade for further improvements that will substantially reduce manufacturing labor, reduce costs of production and increase ease and safety of use of such ladders.